Preparation of dinitrocresols



United States Patent 3,517,074 PREPARATION OF DINITROCRESOLS Mendel T. Gordon and Ernest Frank Silversmith, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed May 10, 1967, Ser. No. 637,360

Int. Cl. C07c 79/28 US. Cl. 260-622 8 Claims ABSTRACT OF THE DISCLOSURE Process for the direct nitration of ortho or para cresol in acetic acid within the temperature range of from 25 to 55 C.

BACKGROUND OF THE INVENTION Dinitrocresols have been known as valuable intermediates and have utility as weed killers. Prior. art methods for the preparation of dinitrocresols have been characterized by one or more disadvantages which include low yield, dangerous procedures, expensive cooling requirements, and production of low quality product contaminated by tars formed during the nitration reaction.

One early prior art method for the preparation of dinitrocresols was the direct nitration of cresol in the presence of glacial acetic acid at a temperature in the range of from 15 to 10 C. This method is disclosed in the Chemical Society Journal Transactions, vol. 127, 1925, page 44 and in the canadian Journal of Chemistry, vol. 31, 1953, page 685.

An improved method which eliminated the requirement for low temperatures involved initial sulphonation of the cresol and then subsequent nitration as disclosed in US. Pat. No. 2,256,195, and US. Pat. No. 2,325,753. This method has the disadvantage of equipment corrosion problems since both sulfuric and nitric acids are present. Stainless steel equipment cannot be used and special corrosion resistant materials must be used to construct the reaction vessel.

Direct nitration of cresol has been carried out at low temperatures for several reasons. As disclosed in British Pat. No. 687,993, laboratory experiments showed that the reaction of cresol and concentrated nitric acid would proceed with detonation-like vehemence. The possibility of explosion in commercial production discouraged the use of direct nitration. It was also recognized in the prior art that the process of direct nitration formed resinous byproducts as a result of oxidation and condensation. The activity of nitric acid as an oxidizing agent is more pronounced at higher temperatures.

The process of the present invention overcomes these prior art problems since it may be conducted in conventional equipment, does not require refrigeration, and the danger of explosion is lessened. Contrary to the prior art, minimal amounts of tar were formed.

SUMMARY OF THE INVENTION Ortho or para cresol is nitrated with 60 to 95% nitric acid in glacial acetic acid medium maintained in the temperature range of from 25 to 50 C. to form dinitro, ortho or para cresol. The nitric acid may be added to a solution of cresol in glacial acetic acid or concurrently with the cresol to the acid. Upon completion of the nitration, water is added and the product recovered.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of this invention is carried out by dissolving Ortho-cresol or para-cresol in glacial acetic acid preheated to 25 to 55 C. The amount of glacial acetic acid employed should be about 3 to 10 times by weight, preferably 3 to 5 times, the amount of cresol to be nitrated.

The solution of cresol and glacial acetic acid is agitated and maintained at 25 to 55 C. while nitric acid of 60 to 95% concentration, preferably to 95%, is added. The stoichiometric amount of nitric acid required for complete nitration is 2 moles per mole of cresol. An excess of 2 to 50%, preferably 2 to 10%, over the stoichiometric amount is desirable.

In large scale production, it may be desirable from the standpoint of convenience to add the concentrated nitric acid in two parts. Each addition consists of at least one mole of acid. The first mole is added at a cooler temperature in the range of 25 to 40 C., then the reaction mixture is heated to a temperature in the range of 40 to 55 C. and the second mole of nitric acid added. A higher temperature is recommended for the last part of the acid since the second intro group does not add to the cresol as readily as the first. After each addition of acid, the reaction mixture is maintained at 25 to 55 C. for about 10 minutes to 2 hours or until completion of the reaction. Water is then added to the reaction mixture in an amount of 1 to 5 parts by weight of water to each part of acetic acid and the mixture is cooled to room temperature. The solid product consisting of substantially pure dinitrocresol is isolated by filtration, washed with water and dried. In another preferred embodiment of the invention the cresol to be nitrated and an equimolar quantity of nitric acid are added concurrently to glacial acetic acid maintained at 25 to 55 C. Such concurrent addition prevents the simultaneous presence of large concentrations of unreacted cresol and nitric acid, thereby averting possible oxidation of the cresol and consequent by-products. Addition of nitric acid is then continued until the remaining mole needed to form dinitrocresol has been added.

The nitric acid and cresol may be added to the acetic acid at any temperature within the 25 to 55 C. range. However, it is preferred to finish the addition at the higher limit of the temperature range, namely, 40 to 55 C. if the addition is started at the lower end of the temperature range. The addition may .be completed within about 10 minutes to 2 hours. Water is then added, the product cooled, filtered, washed, and dried as before.

EXAMPLE 1 Nine hundred and forty-two parts of glacial acetic acid were heated at 45 C. in a reaction vessel with a stirrer. Three hundred parts of p-cresol and 204 parts of nitric acid were added simultaneously at 45 to 50 C. in a period of hour. The rates of addition were proportional to the amounts of reactants, i.e., for each part of pcresol present about 0.68 part of 90% nitric acid was added. The mixture was stirred 5 minutes and 24 8 parts of 90% nitric acid were added at 45 to 50 C. in 35 minutes. The mixture was stirred for an additional 1% hours at 45 to 50 C., after which 1960 parts of water were added in one hour and heating was discontinued. The temperature was 45 C. at the beginning of the water addition and 25 C. at the end.

The solid product was collected by filtration, washed with water and dried. Three hundred and eighty parts of 2,6-dinitro-p-cresol of apparent freezing point of 80.4 C. were obtained for a yield of 69.3% The product contained 97.5% of the theoretical number of nitro groups by TiCl titration and the percent of carbon tetrachloride insolubles was 0.13.

EXAMPLE 2 The procedure of Example 1 was repeated except that the reaction temperature was maintained at 30 C. The

yield of 2,6-dinitro-p-cresl was 75.8% and the product contained 0.037% carbon tetrachloride insolubles.

EXAMPLE 3 A solution of 5.0 parts of p-cresol and 15.7 parts of glacial acetic acid was heated to 40 C. with stirring and 8.8 parts of 70% nitric acid were added drop-wise at 40 to 50 C. The mixture was heated 30 minutes at 50 C. and '15 parts of water were added drop-wise. The mixture was cooled to room temperature and filtered. The solid product was washed with water and dried to 6.64 parts of yellow 2,6-dinitro-p-cresol, M.P. 78 to 79 C., for a yield of 72%.

EXAMPLE 4 The procedure of Example 3 was repeated using 5.0 parts of o-cresol instead of p-cresol. Six and one-half parts of 4,6-dinitro-o-cresol, an orange solid melting at 830 to 83.5 C., were obtained for a yield of 71%.

It is to be understood that the preceding examples are representative and that said examples may be varied within the scope of the total specification, as understood by one skilled in the art, to produce essentially the same results.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof, except as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The nitration of a cresol selected from the group consisting of ortho-cresol and para-cresol with at least about 2 moles, per mole of cresol, of nitric acid of 60 to 95% concentration in about 3-10 parts per weight, based on the weight of cresol, of glacial acetic acid medium maintained in the temperature range of from 25 to 55 C. to form dinitro-cresol.

2. The process of claim 1 in which the reaction mass is maintained in the said temperature range for from 90 minutes to 2 hours.

3. The process of claim 1 in which the dinitro-cresol product is recovered by filtration.

4. The process of claim 1 in which said nitric acid is added to a solution of said cresol and said glacial acetic acid.

5. The process of claim 1 in which said nitric acid and said cresol are added simultaneously to said glacial acetic acid.

6. The process of claim 1 in which said nitric acid is present in an excess of from 2 to 50%.

7. The process of claim 4 in which about one mole, per mole of cresol, of nitric acid is added to said cresol and said glacial acetic acid medium maintained at a temperature in the range of from about to C. to mononitrate said cresol and in which subsequently is added, per mole of cresol, about one additional mole of nitric acid to said medium maintained at a temperature in the range of from about 40 to C. to dinitrate said cresol.

8. The process of claim 5 in which said cresol and about one mole, per mole of cresol, of nitric acid are added simultaneously to said glacial acetic acid medium maintained in the temperature range of from 25 to 0 C. to mononitrate said cresol and in which subsequently is added, per mole of cresol, about one additional mole of nitric acid to said glacial acetic acid medium maintained at a temperature of from 40 to 55 C. to dinitrate said cresol.

References Cited FOREIGN PATENTS 501,818 10/1957 France. 573,768 4/1959 Canada.

OTHER REFERENCES Dutton et al., Canadian J. of Chem, vol. 31, pp. 685- 7 (1953).

Schiemann et al., Chem. Ber., vol. 70, pp. 2400-1 (1937).

Hart et al., J. Am. Chem. Soc., vol. 73, pp. 3179-3182 (1952).

BERNARD HELFIN, Primary Examiner W. B. LONE, Assistant Examiner 

